1. Technical Field
The present invention relates to novel proteolytic enzymes having improved properties for use in detergents. These properties include improved stain removing ability in laundry detergent washing compositions, improved stability in laundry detergents upon storage and improved stability in suds prepared from the detergents.
2. Relevant Literature
Use of enzymatic additives, in particular proteolytic enzymes, in detergent compositions to enable removal of protein based soilings has been amply documented. See for example the published European Patent Applications EP-A-0220921 and EP-A-0232269, U.S. Pat. Nos. 4,480,037 and Re 30,602, and the article "Production of Microbial Enzymes", Microbial Technology, vol. 1 (1979) 281-311, Academic Press.
Detergent compositions may be in a powder, liquid or paste form. They contain one or more anionic, nonionic, cationic, zwitterionic or amphoteric compounds as the detergent active material. Such compounds are described at length in "Surface Active Agents", Vol. II by Schwartz, Perry and Berch, Interscience Publishers (1958). Furthermore, they may include sequestering agents, stabilizing compounds, fragrance compounds and in some cases oxidizing agents, usually called bleaches. Detergent compositions are applied for hard surface cleaning, toilet cleaning, dish washing (either automatic or by hand) and laundry cleaning.
Laundry detergents are generally divided into two major types, liquids and powders. Liquid laundry detergents have high concentrations of surfactants, neutral to moderately alkaline pH and generally do not contain bleaching agents. Powder detergents mostly have high alkalinity (sud pH 9-11); they contain sequestering agents like sodium tripolyphosphate and, depending on the washing habits of the countries where they are sold, they may or may not contain bleaching agents.
Enzymes currently used in detergent compositions are added in liquid suspension, sol or granulate form. For example, in powder detergents the proteolytic enzymes are generally present in an encapsulated form such as prills (e.g. of Maxatase.sup.R and Maxacal.sup.R) or granulates (e.g. of Savinase.sup.R and Alcalase.sup.R). Maxatase and Maxacal are marketed by International Bio-Synthetics B.V. (Rijswijk, The Netherlands), Savinase and Alcalase by NOVO Industri A/S (Bagsvaerd, Denmark). In liquid laundry detergents, enzymes are mostly present in solution.
Proteolytic enzymes are generally difficult to combine with detergent compositions. They must be stable and active during application, for example in removing proteinaceous stains from textile during washing at temperatures ranging from about 10.degree. C. to over 60.degree. C. Furthermore they must be stable for prolonged periods of time during storage in the detergent product. Consequently, enzymes have to be stable and functional in the presence of sequestering agents, surfactants, high alkalinity, in some cases bleaching agents, and elevated temperature. As there exist neither universal laundry detergents nor universal washing conditions (pH, temperature, sud-concentration, water hardness) that are used all over the world, the demands on enzymes may vary based on the type of detergent in which they are used and on the washing conditions.
The conditions governing the stability of enzymes in powder detergents are generally not optimal. For example, during storage of enzyme preparations in powder detergents, despite the apparent physical separation of the enzyme from the detergent matrix by encapsulation of the enzyme, oxidizing agents from the detergent affect the protease and reduce its activity. Another cause of instability of the enzyme in powder detergents during storage, is autodigestion, especially at high relative humidities.
Moreover, oxidizing agents often present in powder detergents have an important drawback on stain removing efficiency during application in laundry cleaning by way of fixation of proteinaceous stains to the fabric. Additionally, these oxidizing agents and other detergent components, like sequestering agents, reduce the efficiency of the protease in stain removal also during the washing process.
In liquid detergents an important problem is rapid inactivation of enzymes, especially at elevated temperatures. As the enzymes are present in the detergent product in solution, this inactivation already takes place in the detergent product during normal storage conditions and considerably reduces the activity of the enzymes before the product is actually used. In particular anionic surfactants, such as alkyl sulfates, in combination with water and builders, tend to denature the enzyme irreversably and render it inactive or susceptible to proteolytic degradation.
Partial solutions for stability problems relating to enzymes in liquid detergents are found in adaptations of the liquid detergent formulation such as the use of stabilizing agents to reduce inactivation of the enzymes. See EP-A-0126505 and EP-A-0199405, U.S. Pat. No. 4,318,818 and U.K. Patent Application No. 2178055A.
Another approach to ensure stability of enzymes in liquid detergents is described in EP-A-0238216, where physical separation between the enzyme molecules and the hostile liquid detergent matrix is achieved by formulation technology. In powder detergents alternative encapsulates have been proposed, see for example EP-A-0170360.
In the aforegoing the conditions are summarized which proteolytic detergent enzymes have to meet for optimal functioning, as well as the limitations of the currently available enzymes for use in detergent compositions. Despite the efforts to ensure enzyme stability in detergent compositions, substantial activity loss is still encountered under normal conditions of storage and application.
Identification and isolation of new enzymes for a certain intended application, such as use in detergents, can be performed in several ways. One way is screening for organisms or microorganisms that display the desired enzymatic activity, isolating and purifying the enzyme from the (micro)organism or from a culture supernatant of said (micro)organism, determining its biochemical properties and checking whether these biochemical properties meet the demands for the application. If the identified enzyme cannot be obtained from its natural producing organism, recombinant DNA techniques may be used to isolate the gene encoding the enzyme, express the gene in another organism, isolate and purify the expressed enzyme and test whether it is suitable for the intended application.
Another way of obtaining new enzymes for an intended application is the modification of existing enzymes. This can be achieved inter alia by chemical modification methods (see I. Svendsen, Carlsberg Res. Commun. 44 (1976), 237-291). In general these methods are too nonspecific in that they modify all accessible residues with common side chains, or they are dependent on the presence of suitable amino acids to be modified, and are often unable to modify amino acids difficult to reach, unless the enzyme molecule is unfolded. Therefore, the enzyme modification method through mutagenesis of the encoding gene is thought to be superior. Mutagenesis can be achieved either by random mutagenesis or by site-directed mutagenesis. Random mutagenesis, by treating a whole microorganism with a chemical mutagen or with mutagenizing radiation may of course result in modified enzymes. In this case strong selection protocols must be available to search for the extremely rare mutants having the desired properties. A higher probability of isolating mutant enzymes by random mutagenesis can be achieved, after cloning the encoding gene, by mutagenizing it in vitro or in vivo and expressing the encoded enzyme by recloning of the mutated gene in a suitable host cell. Also in this case suitable biological selection protocols must be available in order to select the desired mutant enzymes, see International Patent Application WO 87/05050. These biological selection protocols do not specifically select enzymes suited for application in detergents.
The most specific way of obtaining modified enzymes is by site-directed mutagenesis, enabling specific substitution of one or more amino acids by any other desired amino acid. EP-A-0130756 exemplifies the use of this technique for generating mutant protease genes which can be expressed to give modified proteolytic enzymes.
Recently the potential of oligonucleotide mediated site-directed mutagenesis has been demonstrated through the use of mutagenic oligonucleotides synthesized to contain mixtures of bases at several positions within a target sequence. This allows a number of different mutations to be introduced at a specific part of a DNA sequence by using a single synthetic oligonucleotide preparation as exemplified by (Hui et al., EMBO J. 3 (1984) 623-629, Matteucci et al., Nucl. Acids Res. 11 (1983) 3113-3121, Murphy et al., Nucl. Acids Res. 11 (1983) 7695-7700, Wells et al., Gene 34 (1985) 315-323, Hutchinson et al., Proc. Natl. Acad. Sci. USA 83 (1986) 710-714 and F. M. Ausubel, Current Protocols in Molecular Biology 1987-1988, Greene Publishers Association and Wiley, Interscience, 1987.
Stauffer et al., J. Biol. Chem. 244 (1969) 5333-5338 has already found that the methionine at position 221 in Carlsberg subtilisin is oxidized by H.sub.2 O.sub.2 to methionine sulfoxide and is responsible for a dramatic decrease of the activity.
As a result of both the methods of random and site-directed mutagenesis for generating modified enzymes, mutants derived from the serine protease of Bacillus amyloliquefaciens, also called "subtilisin BPN'", were isolated and characterized. In WO 87/05050 a mutant subtilisin BPN' is disclosed with enhanced thermal stability. In EP-A-0130756 is described that site directed mutagenesis of methionine at position 222 in subtilisin BPN' by all 19 possible amino acids, using the so-called "cassette mutagenesis" method, may result in enzymes resistant towards oxidation by H.sub.2 O.sub.2. In the latter case, however, most mutants had low proteolytic activity. The best mutants found were M222A and M222S, which had specific activities of 53% and 35%, respectively, compared to the native subtilisin BPN', see Estell et al., J. Biol. Chem. 260 (1985) 6518-6521.
Prior work on generating modified proteases shows that subtilisin BPN' mutants with altered stability properties and altered kinetic properties can be obtained; see the literature referred to above and other references, for example Rao et al., Nature 328 (1987) 551-554, Bryan et al., Proteins 1 (1986) 326-334, Cunningham and Wells, Protein Engineering 1 (1987) 319-325, Russell et al., J. Mol. Biol. 193 (1987) 803-819, Katz and Kossiakoff, J. Biol. Chem. 261 (1986) 15480-15485, and the reviews by Shaw, Biochem. J. 246 (1987) 1-17 and Gait et al., Protein Engineering 1 (1987) 267-274. However, none of these references have led to the industrial production of proteolytic enzymes with improved wash performance and stability in laundry detergents. None of the modified proteases have been shown to be of commercial value so far and superior to presently used detergent enzymes under relevant application conditions.